John C. Walker
Director of Biological Sciences
Curators’ Distinguished Professor of Biological Sciences
PhD, 1985 University of Georgia
|Office:||321 Tucker Hall|
Molecular mechanisms regulating cellular signaling in plants
Research descriptionMulticellular organisms need to carry out many processes in a coordinated manner to sense and respond to both external and internal signals in an intricate and precise way. Multi-step signal transduction creates the necessary complexity for refined regulation of a cell's response to developmental signals and its environment. A common way cells relay molecular messages is by reversible protein phosphorylation; protein kinases add phosphates to their target protein(s) and protein phosphatases remove them. Cells can begin this process with receptor protein kinases, using phosphorylation status to transduce external messages into the cell. A plethora of candidate receptor protein kinases have been found in plants, but only a few have been investigated. Function for the plant receptor-like kinases (RLKs) has been shown in various biological processes such as development, disease resistance and self-incompatibility.
There are several hundred RLK genes and they represent the largest group of cell surface receptors in plants. The 1999 report of the NSF-Sponsored Workshop: New Directions in Plant Biological Research points out the RLKs represent unexpected discoveries derived from the Arabidopsis genomic sequence. The report states, "What are the roles of the hundreds of these proteins? Their existence implies a massive network of cell-cell and environment-plant communication, via a series of ligands yet to be discovered. Understanding this network will give us an entirely new view of plant development, environmental response, and organismal integration”. Our research is directed toward understanding the function of the RLK genes.
We are using the approaches of functional genomics and proteomics to understand RLK function. We have ongoing projects to 1) Isolate and characterize loss-of-function and gain-of-function mutations; 2) Determine the patterns of expression of the mRNAs, and establish the cellular and subcellular locations of these receptors by use of green fluorescent protein fusions; 3) Define the regulatory networks that mediate signaling by these protein kinases by screening for genetic modifiers and interaction partners. Although we are not yet able to describe an entire signal transduction cascade for any one RLK, these approaches promise to provide important insights into the molecular mechanisms by which the receptor protein kinases control development and adaptive responses in plants.
Patharkar, O.R., Walker, J.C. Advances in abscission signaling (2018) Journal of Experimental Botany, 69 (4), pp. 733-740. DOI: 10.1093/jxb/erx256
Patharkar, O.R., Gassmann, W., Walker, J.C. Leaf shedding as an anti-bacterial defense in Arabidopsis cauline leaves (2017) PLoS Genetics, 13 (12), art. no. e1007132, DOI: 10.1371/journal.pgen.1007132
Patharkar, O.R., Walker, J.C. Core mechanisms regulating developmentally timed and environmentally triggered abscission (2016) Plant Physiology, 172 (1), pp. 510-520.
Baer, J., Taylor, I., Walker, J.C. Disrupting ER-associated protein degradation suppresses the abscission defect of a weak hae hsl2 mutant in Arabidopsis (2016) Journal of Experimental Botany, 67 (18), pp. 5473-5484.
Patharkar, O.R., Macken, T.A., Walker, J.C. Serine 231 and 257 of Agamous-like 15 are phosphorylated in floral receptacles (2016) Plant Signaling and Behavior, 11 (7), art. no. e1199314,
Taylor I, Wang Y, Seitz K, Baer J, Bennewitz S, Mooney BP, Walker JC: Analysis of Phosphorylation of the Receptor-Like Protein Kinase HAESA during Arabidopsis Floral Abscission. PLoS ONE 2016, 11(1), art. no. e0147203,
Patharkar OR, Walker JC: Floral organ abscission is regulated by a positive feedback loop. Proceedings of the National Academy of Sciences of the United States of America 2015, 112(9):2906-2911.
Li J, Hou J, Sun L, Wilkins JM, Lu Y, Niederhuth CE, Merideth BR, Mawhinney TP, Mossine VV, Greenlief CM et al: From gigabyte to kilobyte: A bioinformatics protocol for mining large RNA-Seq transcriptomics data. PLoS ONE 2015, 10(4).
Niederhuth CE, Patharkar OR, Walker JC: Transcriptional profiling of the Arabidopsis abscission mutant hae hsl2 by RNA-Seq. BMC Genomics 2013, 14(1).
Valdivia ER, Hertweck KL, Cho SK, Walker JC: DVL/RTFL. In: Handbook of Biologically Active Peptides. 2013: 15-19.
Taylor I, Seitz K, Bennewitz S, Walker JC: A simple in vitro method to measure autophosphorylation of protein kinases. Plant Methods 2013, 9(1).
Niederhuth CE, Cho SK, Seitz K, Walker JC: Letting go is never easy: Abscission and receptor-like protein kinases. Journal of Integrative Plant Biology 2013, 55(12):1251-1263.
Meng X, Wang H, He Y, Liu Y, Walker JC, Torii KU, Zhang S: A MAPK cascade downstream of ERECTA receptor-like protein kinase regulates Arabidopsis inflorescence architecture by promoting localized cell proliferation. Plant Cell 2013, 24(12):4948-4960.
Valdivia ER, Chevalier D, Sampedro J, Taylor I, Niederhuth CE, Walker JC: DVL genes play a role in the coordination of socket cell recruitment and differentiation. Journal of Experimental Botany 2012, 63(3):1405-1412.
Honors & Awards
Selected honors and awards
Curators Professor, University of Missouri 2014
Excellence Award, Interdisciplinary Plant Group, MU 2012
Fellow, American Association for the Advancement of Science 2004
Chancellor’s Award for Outstanding Faculty Research and Creative Activity in Biological Sciences 1997
March 11, 2015
Feb. 24, 2015
Molecular feedback loop gives clues to how flowers drop their petals
Jan. 28, 2015
Sept. 2, 2014
John C. Walker Appointed MU Curators’ Professor
Aug. 5, 2014
Aug. 5, 2014
Nov. 2, 2012
Five Biology Professors Celebrated at Faculty Recognition Banquet
Sept. 18, 2012
Professor John Walker Receives IPG Award of Excellence